Inductive electric apparatus

ABSTRACT

An inductive electric apparatus which comprises a polycylic hydrocarbon oil mixture having a flash point of more than 150*C and consisting of polycyclic naphtenic hydrocarbons having two to five rings and polycyclic aromatic hydrocarbons having two to four rings, each side chain alkyl group attached to said rings having not more than four carbon atoms, an electroconductive coil and a cellulose insulator in combination. The inductive electric apparatus can have a larger increase in allowable temperature than that of a combination of the ordinary hydrocarbon insulating oil and the cellulose insulator, and accordingly it is possible to make the apparatus smaller and lighter.

[ INDUCTIVE ELECTRIC APPARATUS lnventors: Akin Miyoshi; Tornio Nagaoka;

Hasaaki Takahashl; Kensuke Okuda, all of Tokyo, Japan [731 Assignees: Hitachi, Ltd.; Kureka Industry Co.,

both of Tokyo. Japan [22] Filed: Dec. 28, 1970 [21] Appl. No.: 101,686

Foreign Application Priority Data Dec. 29, 1969 Japan 44/1120 [1.8. Ci 340/1461 AJ, 235/6l.1l E. 235/6l.7 A

Int. Cl. H01! 27/02 Field of Search 208/14, 19; 336/94; 252/63 [56] References Cited UNITED STATES PATENTS 2,846,372 8/1958 Schneider et a1. 208/14 [451 Aug. 14, 1973 6/1963 Schieman 208/19 Primary Examiner-Herbert Levine AttorneyCraig, Antonelli, Stewart & Hill ABSTRACT An inductive electric apparatus which comprises a polycylic hydrocarbon oil mixture having a flash point of more than 150C and consisting of polycyclic naphtenic hydrocarbons having two to five rings and polycyclic aromatic hydrocarbons having two to four rings, each side chain alkyl group attached to said rings having not more than four carbon atoms, an electroconductive coil and a cellulose insulator in combination. The inductive electric apparatus can havea larger increase in allowable temperature than that of a combination of the ordinary hydrocarbon insulating oil and the cellulose insulator, and accordingly it is possible to make the apparatus smaller and lighter.

7 Claims, 3 Drawing Figures HEAT/IVG/A/POL YCYL/C HYDPOCARBOVOL MMUREJ] ,Hsar/ma/v POLYCYL/C HYDQOCAABO/VO/L MMLREH s3 )HEAfi/VG/NMYCYL/CHYDPOCARBOVOL MDKTMGE] E a E 60- S (I) g l-E477/V6l/VMl/VHB4L wwfl/va OIL a 20- E v SAMPLE 05mm! KRAFrm E/P E 0 /0 29 3'0 5'0 tion. Asis well known, these insulatingmaterials have" a poor: heat. resistance, and when these materials are heated tomore than some temperature bya heat release. ofthe coil duringJthe'service-period, these insulating materials undergoheat decomposition and rapid deterioration. As aresult;.organicacids and sludge are" formed from the insulating. oil, and the mechanical strengthofthe cellulosic materialis'lowered. That is, the cellulosic: material fails to -withstand' amechanical impact generated at. the short' circuit of the coil; and consequentlyloses itsproper function; Though there: have been already employed: enamel coated= electric wires having: heat resistances-equivalent or superior to grade B-of the insulatiomcode for'the coils the-overall' insulatingclassification of aninductive electric apparatus usingaan insulatingtoil of mineral oilorigin arid a cel= lulosic material as theinsulating.materialisgrade A,

and therefore the allowable temperature'increase at the: ambient: temperature of 40 6 is repressed to '5 Furthermore, theflashpoint of th'e insulating oil of mineral oil 'originnow employed is about-l40Cand the Grade B insulation (allowable temperature incre'aseto 75C is not applicable to the prior art inductive elec tric apparatus in-this respect, either.

Recently, every-effort has been made to'improve the heat resistancezof the insulating material to 'be used so as to make'smaller and lighter such inductive electric apparatuses as transformers, et'c;, and asone of the measures, there have been developedvarious antioxidants'to be addedjto the insulatingoil: However; when an oil admixed withthe antioxidant'isused in the'inductive electric-apparatus, it is difficultto control the antioxidant to be added to aproperamount in exchangingthe oil deteriorated during the service period,- and-furthermore there is aproblemin the maintenanceof the apparatus: Furthermore, the antioxidant is not useful for enhancingithe flash point of'the oil itself.

vOn the other hand, cyanoethylated paper orpaper treated'with'amines or other chemical-admixed paper has been developed toimprove the heat resistance-of the cellulosic insulatingv materialssuch' as kraft paper,

but a costincrease of the paperordeteriorationofme chanical properties of the paper itself resulting. from the special treatment of the paper has beena problem; Therefore; .these papers have not yet been widely utilized.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inductive electric apparatus insulated by a novel synthetic' insulating hydrocarbon oil and cellulosic material'having a good heat resistance.

Other objectof the present invention is to provide an inductive electric apparatus capable of undergoing continuousservice at a high temperature corresponding-to or approximate to'that of Grade'B by using a relatively cheap insulating material.

Another object of the presen'tinvention is toprovide a thermally stable, inductive electric apparatus having agood reliability. l 1 k Furtherobjectof the present invention is to provide an improved inductive electric apparatuscapable of controlling a heat deterioration in an insulating oil without applying'any special treatment to the cellulosic insulating material to intensify the heat resistance.

Stillfurther object of the present invention is to provide an inductive electric apparatus of easy maintenance without adding any antioxidant at the exchange Otherobjects of the present inventionwill be readily understandable from the'following explanation.

According to the present invention, an inductive electricapparatus comprises an oil of polycyclic hydrocarbonmixture having a-flashpoint of 150C or more and-consisting of (A) "polycyclic naphthenic hydrocarbons having two to five rings and'(B) polycyclic aromatic hydrocarbons having two to'four rings as a syntheticinsulating oil, each side chain alkylgroup at tached to'the rings having not-more than four carbon atoms, preferably a'mixing ratio of said (A) to (B) being ina range of 50 2 50 7O 30 by volume; a cellulosic material; an electrically conductive coil, the'cellu losic material being combined with the electrically conductve-coil, and the'cellulosic material and the electrically conductive coilbeing immersed in the insulating oil'and being constantly in'contact therewith.

BRIEF DESCRIPTION OF THE DRAWINGS- FIG. 1 is an elevation of partially cut-away power transformer shown as one embodiment of the present invention.

FIG. 2 andFIG. 3 are diagrams showing relations between an efiective tensile strength of the insulating paper and a heating time when heat deterioration tests are carried out with the insulating paper and said oil of polycyclic hydrocarbon mixtures to be used in'the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A power transformer as shown in FIG. 2 comprises an oil-sealed tank I; an iron core'2, a primary coil 3, a secondary coil 4 and an insulating oil Sfilled around the iron core and coils. The coils 3 and 4 are prepared by coiling an electrically conductive material coated with an enamel, for example, a polyvinyl formal resin in a plurality of layers, while inserting a cellulosic mate rial such as a kraft paper between the layers according to the well known method. An insulating layer 6 between the coil 3 and the'iron core 1', an insulating material 7 between the coils 3 and'4, and an outermost insulating material 8 of the coil 4 are also made from a cellulosic'material such as the kraft paper.

These cellulosic materials are immersed in the insulating oil 5, together with the coils, and are always kept in contact with the insulating oil 5.

A small amount of air may be retained over the oil surface within the tank 1, but it is more preferable that an inert gas such as nitrogen is sealed over the oil surface in place of the air.

As the insulating oil 5, the above-mentioned oil of polycyclic hydrocarbon mixture is used.

As a result of experiments and studies, the present inventors have newly found that said oil of polycyclic hydrocarbon mixture has a high flash point corresponding to the Grade B insulation and an excellent oxidation stability, and further that the heat deterioration of the cellulosic material takes place remarkably less in said oil of polycyclic hydrocarbon mixture than in the conventional insulating oil of hydrocarbon origin.

The component (A) of said oil of polycyclic hydrocarbon mixture, that is, polycyclic naphthenic hydrocarbons, is a mixture of a plurality of polycyclic hydrocarbons having two to five rings prepared by thermally cracking petroleum hydrocarbons at 700 2,300C, hydrogenating the resulting tar fraction rich in polycyclic aromatics in the presence of a catalyst or desulfurizing said tar fraction, if necessary, then alkylating the resulting with lower olefins in the presence of a catalyst and further hydrogenating the resulting product in the presence of a catalyst according to methods of US. Patent application Ser. No. 800,710 (assignee: Kureha 1969 and US. Patent application Ser. No. 23,962 (assignee: Kureha Chemical Industry Co., Ltd.) filed on Mar. 30, 1970, to obtain a plurality of polycyclic hydrocarbons, or a mixture of a plurality of lower alkyl derivatives of the polycyclic hydrocarbons, or a mixture of the polycyclic hydrocarbons and the lower alkyl derivatives thereof, and has the following properties:

Specific gravity (r1 0.85 0.99

(values measured at 4C are converted to those at Refractive index (n 1.45 1.60

(values measured at C by D spectrum of nitrogen gas) Viscosity (C) 10 40 CST Atomic ratio of hydrogen/carbon 1.75 2.00

Flash point 125C or higher Pour point (30C) (60C) The other component (B) of said oil of polycyclic hydrocarbn mixture, that is, polycyclic aromatic hydrocarbons, is a mixture of a plurality of polycyclic hydrocarbons of two to four rings prepared by thermally cracking petroleum hydrocarbons at 700 2,300C, desulfurizing the resulting tar fraction rich in polycyclic aromatics, if necessary and then subjecting theresulting to lower olefins in the presence of a catalyst of silica-alumina system, or zeolite system, to obtain a mixture of a plurality of polycyclic aromatic hydrocarbons, or a mixture of lower alkyl derivatives of the polycyclic hydrocarbons, or a mixture of the polycyclic hydrocar-v bons and the lower alkyl derivatives thereof, and has the following properties:

Specific gravity ((1 1.00-1.20

Refractive index (n 1.50 1.68

Viscosity (30C): 10-25 CST Flash point: 150C or higher Pour point: -40C or less Said oil of polycyclic hydrocarbon mixture consisting of said two components is different from the conventional insulating oil of mineral oil origin, and is'a novel hydrocarbon insulating oil quite free of thermally unstable paraffins and isoparaffins. Among others, .it has been found that the oil of polycyclic hydrocarbon mixture having a mixing ratio of the component A to the component B of 50 50 30 by volume has a very preferable property for an insulating oil for such in inductive electric apparatus as a transformer. its typical physical properties are given below:

Specific gravity (11 0.900 -'l.050

Refractive index (n,,) 1.45 1.58

(values measured at 25C by D spectrum of nitrogen gas) Viscosity, CST (20C) 2 10 120 Pour point, C: 10 or less Flash point, C: 150 210 I Dielectric constant (C) 2.00 3.00

Dielectric loss, (80C): 0.002 0.30

Volume resistivity, 0 cm (80C) 10 l0 Dielectric breakdown voltage, kV/2.S mm 40 or higher To compare the heat resistance of said oil of polycyclic hydrocarbon mixture with that of the insulating oil now employed, difierent samples 1, I1 and 111 of said oil of polycyclic hydrocarbon mixture were prepared, and the initial characteristics and deterioration characteristics of the samples 1, 11 and Ill and the insulating oil of mineral oil origin now employed [an equivalent to the insulating oil set forth in Japanese industrial Standard (M8) N0. 2] were measured. As the initial characteristics, a flash point, viscosity, dielectric breakdown voltage and volume resistivity, which are important characteristics for an insulating oil for the transformer, were measured and their results are given in Table 1.

As is seen from Table l, the flash point of said oil of polycyclic hydrocarbon mixture is as high as 160C or higher than 160C, which corresponds to the value of the Grade B insulation.

" TABLE 1 i Insulating oil now Sample I II III employed Structure:

Ring number of polycyclic naphthenic hydrocarbons, A 3-5 4-5 3-4 Ring number of po ycycllc aromatic hydrocarbons, B 23 34 2-3 Mixing ratio of A/B 70/30 70/30 50/50 Flash point, C 170 176 166 142 Viscosity, CST: v

30 79. 0 100. 2 63. 3 18. 5 80C 8.1 11.5 6.2 3.0 Dielectric breakdown voltage, kv./2.5 mm- 57. 7 58. 5 60. 0 55. 0 Volume resistivity, 1.9)(10 1. 1X10 4X10" 0cm. (80 C) 4.0X10

The deterioration characteristics of samples are compared in terms of the amount of sludge formed and total acid value after the heating at C for 100 hours, at C for 100 hours, and at C for 100 hours, respectively. The results are shown in Table 2.

lt has been found that saidoil of polycyclic'hydrocarbon-mixture has less deterioration even after the heating at 150C for 100 hours than the insulating oil of mineral oil origin now=':employed after the heating at 120C for 100 hourspand has an. excellent oxidation stability. 7

As is clear. from the foregoing explanation and test results, the present inductive electric apparatus based on acombination of said oil of polycyclic hydrocarbon mixture and a cellulosic insulating material is workable at a high temperature equal to or approximate to that of the Grade B insulation for a long period of tinie, and

TABLE 2 Sample Insulating oil now I II III employed Total acid Total acid Total acid Total acid Sludge value (mg. Sludge value (in Sludge value (mg. Sludge va lne (mg. Items measured (percent) KOH (percent) KOH/g. (percent) KOH/g.) (percent) LOH/g.)

Condition for measurement:

0.04 0.08 0.04 0.06 0.14 0. 31 0. 06 0. 10 0.05 0.03 0. 39 0. ST '0. l3 0. 0.26 0.10 0.063 0.36

The present synthetic insulating oil was heated together' with a cellulosic material to determine the influence of the deterioration of oil upon the cellulosic material. 7'5 g:each of insulating papersoftypical cellulosic, materials (the ordinary kraft-paper and cyanoeth-' ylated paper) was placed:in individual vessels together with 800 cc eachxof saidoilof polycyclic-hydrocarbon mixture.(Samplesl; llan'd'lll) and the insulating oil of mineral oil origin: now employed (-anequivalent' to theinsulating-oilset forth inzJlS No. 2') individually andthe vessels-were.sealedJwhile-retaining the air above the oil surface and. heated at 130C for. 60-days. During said period-of 60.-days, changes in tensile strength of the insulating papers were measured. The results are shown in FIGS. 2 andz3t Thatis to say, in thecase of the ordinary kraft paper which wasnot subjected to a treatment for intensifying the heat resistance, the tensile strength'afterthe heating for 60 days drops to 20 percentor less of the initial-value in the insulatingoil now. employed, but retains. about 50 percent of the initial tensile strength, even after the heating for 60 days, in said oil of polycyclic hydrocarbon mixture, which is almost equal to the effective tensile strength of the cyanoethylated paper after the heating for 60 days in the insulating oil-now employed. A combination of the cyanoethylated paper with said'oil of'polycyclic hydrocarbon mixture can increase the effective tensile strength after the heating for 60 days to 70 percent or higher of the initial tensile strength. It is seen from these results, that even a service temperature of the ordinary kraft paper having a relatively low heat resistance can be elevated, when used together with said oil of polycyclic hydrocarbon mixture, almost to the service temperature of the cyanoethylated paper when used together with the insulating oil of mineral oil origin now employed.

The present inventors have newly. found that the present synthetic insulating oil has an unexpectedef v ing oil, and a cellulosic material combined with said coil, said insulating oil being a polycyclic hydrocarbon oil mixture having a flash'point of 150C or higher and consisting of a component (A) comprising polycyclic fect upon an increase in the heat resistance of the insu .lating paper when used together. Though a still further. study will be necessary for elucidating the reason why such an effect can be brought about upon the increase 'in the heat resistance of the insulating paper, the pres ent inventors assume that a good oxidation stability of said oil of polycyclic hydrocarbon mixture helps to decrease the deterioration of the insulating paper due to the decomposition product, for example, organic acids, etc., of the insulating oil.

as a result, the entirety of the present apparatus can be made considerably smaller and lighter by the elevation of the allowable service temperature than the entirety of the conventional inductive electric apparatus based on the conventional insulating oil of mineral oil origin and the cellulosic insulating material. I

When the present apparatus isused'at a service temperature equal to that of the Grade A insulation, the heat-resisting life of the present apparatus isremarkably prolonged and the reliability of the apparatus is greatly enhanced. Furthermore, in replacing the insulating oil by a user, only the specified kind of insulating oil is used according to the present invention. Thatis, there'is no trouble in maintenance, as seen in the case that an antioxidant is added to he insulating oil now employed. Furthermore, the heat resistance not only of the-oil itself, but also of the cellulosic material used'together with the oil, can be increased according to the present invention, and a good heat resistance substantially equivalent to that of the cyanoethylated paper now employed can be efiectively brought about even by using the ordinary kraft paper of a low cost and a high initial tensile strength.

Said oil of polycyclic hydrocarbon mixture can be used properly in a mixture of the insulating oil of mineral oil origin now employed, and such mode of practice is, of course, included in the scope of the present invention.

Since said oil of polycyclic hydrocarbon mixture can be prepared from such abundant raw materials as tar fraction produced in the course of petroleum refining, said oil can be obtained at a lower cost as an insulating oil having a higher heat resistance than other inorganic synthetic insulating oil.

What is claimed is:

1. An inductive electric apparatus, which comprises an oil-sealed tank, an insulating oil filled in saidtank, an electrically conductive coil immersed in said insulatnaphthenic hydrocarbons having two to five rings or their alkyl derivatives and mixtures thereof and component (B) comprising polycyclic aromatic hydrocarbons having two to four rings or their alkyl derivatives and mixtures thereof at a mixing ratio of A/B of 50:50

:30 by volume, and each alkyl group attached to said rings of components (A) and (B) having not more than four carbon atoms.

2. An inductive electric apparatus according to claim 1, wherein said cellulosic material is selected from kraft paper and cyanoethylated paper.

3. An inductive electric apparatus according to claim 1, wherein said component A of the polycyclic naphthenic hydrocarbons comprises a mixture of a plurality of polycyclic hydrocarbons having two to five rings, or a mixture of a plurality of lower alkyl derivatives thereof, or a mixture of the polycyclic hydrocarbons and the lower alkyl derivatives thereof and has a specific gravity (11 of 0.85 0.99, refractive index (n of 1.45 1.60, a viscosity (30C) of 40 CST, an atomic ratio of hydrogen to carbon of 1.75 2.00, a flash point of 125C or higher and a pour point of 30 to 60C.

4. An inductive electric apparatus according to claim 1, wherein said component B of the polycyclic aromatic hydrocarbons comprises a mixture of a plurality of polycyclic aromatic hydrocarbons having two to four rings, a mixture of a plurality of lower alkyl derivatives thereof, or a mixture of the polycyclic aromatic hydrocarbons and the lower alkyl derivatives thereof, and has a specific gravity ((1 of 1.00 1.20, a refractive index (n of 1.50 1.68, a viscosity (50C) of 10 25 CST, a flash point of 150C or higher and a pour point of 40C or less.

5. An inductive electric apparatus according to claim 1, wherein said insulating oil is an oil of polycyclic hydrocarbon mixture consisting of component (A) comprising polycyclic napthenic hydrocarbons having three to five rings and component (B) comprising polycyclic aromatic hydrocarbons having two to three rings at a mixing ratio of A/B of /30 by volume.

6. An inductive electric apparatus according to claim 1, wherein said insulating oil is an oil of polycyclic hydrocarbon mixture consisting of component (A) comprising polycyclic naphthenic hydrocarbons having four to five rings and component (B) comprising polycyclic aromatic hydrocarbons having three to four rings at a mixing ratio of (A)/(B) of 70/30 by volume.

7. An inductive electric apparatus according to claim 1, wherein said insulating oil is an oil of polycyclic hydrocarbon mixture consisting of component (A) comprising polycyclic naphthenic hydrocarbons having three to four rings and component (B) comprising polycyclic aromatic hydrocarbons having two to three rings at a mixing ratio of (A)/(B) of 50/50 by volume. l

f f UNITED STATES PATENTOFFICE CERTIFICATE' OF CORRECTION Patent No-, U. S. e 3, 7 53, 188- I Dated I August 14, 1973 V Akira MI OSH TOmiO NAGAOKA, Masaaki .TQAKAHASHI and Kensuke OKUDA I e s i I It is certified that; error appears in I the above-i and that said Letters Patent; are hereby corrected as shown below:

In\ rento r(s) dentified patent In Column l,' I

after line 2f, delete "Hasaali" and insert --Masaaki, in 1in-e'5,' di eK115559355 in sr t Kur eha- I in line 10", '4ie 1 e' -*'D c; 29',-1969 Japanf. Q .44/1 1 20 and insert -Dec. 29, 1969 .45/*1'1-2"o a s gned.a z ledflhis zsui day iof De c e mber 1 73:}

(SEAL) I Attest': EDWARD M.FLETCHE R;JR. I RENE D. TEGTMEYER.

Attesting Officer Acting. Commissioner of Patents :U-SCOMM-DC scan-Pu I FORM P0 050 (IO-69) UNITED STATES PATENTOFFICE CERTIFKCATE OF CORRECTION Patent: No. U. S. 3, 188 D t d August 14, 1973 Inventor) Akir-a MIYOSHI,T0miO NAGAOKA, Masaaki .TAKAHASHI and Kensuke OKUDA It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 1; h

after line 2 delete "Hasaak i" and insert Masaaki-, in line 5, delete "Kureha" and insert -Kureha---, I

in line 10, delete' Deo. 29, 1969 Japan; Q .44/1120 and insert -Dec. 29, 1969 Ja an.-......'... .45/"1120--=- Signed andsealed this 25th day of December 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. I I RENE D. TEGTMEYER Attesting Officer 7 1 Acting Commissioner of Patents uscowu-ocpoan-pn FORM P0-105O (\O-69) 

2. An inductive electric apparatus according to claim 1, wherein said cellulosic material is selected from kraft paper and cyanoethylated paper.
 3. An inductive electric apparatus according to claim 1, wherein said component A of the polycyclic naphthenic hydrocarbons comprisEs a mixture of a plurality of polycyclic hydrocarbons having two to five rings, or a mixture of a plurality of lower alkyl derivatives thereof, or a mixture of the polycyclic hydrocarbons and the lower alkyl derivatives thereof and has a specific gravity (d415) of 0.85 - 0.99, refractive index (nD20) of 1.45 - 1.60, a viscosity (30*C) of 10 - 40 CST, an atomic ratio of hydrogen to carbon of 1.75 - 2.00, a flash point of 125*C or higher and a pour point of -30* to -60*C.
 4. An inductive electric apparatus according to claim 1, wherein said component B of the polycyclic aromatic hydrocarbons comprises a mixture of a plurality of polycyclic aromatic hydrocarbons having two to four rings, a mixture of a plurality of lower alkyl derivatives thereof, or a mixture of the polycyclic aromatic hydrocarbons and the lower alkyl derivatives thereof, and has a specific gravity (d415) of 1.00 - 1.20, a refractive index (nD20) of 1.50 - 1.68, a viscosity (50*C) of 10 - 25 CST, a flash point of 150*C or higher and a pour point of -40*C or less.
 5. An inductive electric apparatus according to claim 1, wherein said insulating oil is an oil of polycyclic hydrocarbon mixture consisting of component (A) comprising polycyclic napthenic hydrocarbons having three to five rings and component (B) comprising polycyclic aromatic hydrocarbons having two to three rings at a mixing ratio of A/B of 70/30 by volume.
 6. An inductive electric apparatus according to claim 1, wherein said insulating oil is an oil of polycyclic hydrocarbon mixture consisting of component (A) comprising polycyclic naphthenic hydrocarbons having four to five rings and component (B) comprising polycyclic aromatic hydrocarbons having three to four rings at a mixing ratio of (A)/(B) of 70/30 by volume.
 7. An inductive electric apparatus according to claim 1, wherein said insulating oil is an oil of polycyclic hydrocarbon mixture consisting of component (A) comprising polycyclic naphthenic hydrocarbons having three to four rings and component (B) comprising polycyclic aromatic hydrocarbons having two to three rings at a mixing ratio of (A)/(B) of 50/50 by volume. 